Portable video camera having power saving control of stepping motors

Description

[0001] This invention relates to a portable video camera using stepping motors in focusing and zooming mechanisms.

[0002] Many of portable video cameras, in particular of small-scaled ones for home use, include built-in automatic focusing mechanism and zooming mechanism for easier video camera work. Automatic focusing and zooming mechanisms include lens drive means, and they are generally driven by stepping motors as described, for example, in JP-A-5,281,459 on which the pre-characterising portion of claim 1 is based.

[0003] Stepping motors, in general, are essentially driven by a rectangular wave. However, stepping motors driven by a rectangular wave, in operation, generate noise caused by vibrations or higher harmonics. Therefore, most of stepping motors incorporated into video cameras are driven by a sine wave.

[0004] As explained in EP-A-0,571,289 driving by sine wave is effected on the basis of data preliminarily stored in ROM without actually generating a sine wave. The ROM stores data indicating duty ratios of rectangular waves corresponding to sine waves taken by sampling at appropriate intervals. For example, the duty ratio is determined as 50% at angle 0 (rad), 100% at π/2, 0% at 3π/2, et seq. The stepping motor is driven by a rectangular wave generated on the basis of the data. At this time, the rectangular wave is smoothed into a sine wave by a bridge circuit for driving the stepping motor or by the coil of the motor itself.

[0005] Data stored in ROM corresponds to a sine wave. Therefore, the ROM need not store data of the full cycle from 0 to 2π, but may store, for example, data of only 1/4 cycle from 0 to π/2. When the stepping motor is driven, during 0 to π/2, data read out from ROM is used directly, and during π/2 to π, data stored in ROM is read out in the opposite sequence from that for 0 to π/2. During π to 3π/2, data of 0 to π/2 stored in ROM is read out in the normal sequence but inverted in sign. During 3π/2 to 2π, data for 0 to π/2 is read out in the opposite sequence and assigned with the opposite sign. In this manner, by changing the order of reading data and/or changing the sign, where necessary, data of the full cycle from 0 to 2π can be produced from data of 0 to π/2 alone. When a stepping motor is driven by a sine wave, the cycle of the sine wave is modified to change the driving speed of the motor into a value for high-speed driving, low-speed driving, or the like. In the accompanying drawings, Fig. 6 shows sine waves of different cycles for different driving speeds. As illustrated, the cycle is short for high-speed driving and long for low-speed driving. The amplitude of the sine wave is constant regardless of the speed.

[0006] Fig. 7 shows a conventional circuit arrangement for driving a stepping motor. The stepping motor used here is of a PM (permanent magnet) type 2-phase-excited bipolar driving which is generally used for driving lenses of video cameras, floppy disk driving systems, and so forth.

[0007] MCU 100 supplies a read clock signal and an UP/DOWN signal to an address counter 101. Based on these signals, address data for reading out sine wave data from ROM 102 is supplied from the address counter 101 to ROM 102.

[0008] The read clock determines the frequency of the sine wave data read out from ROM 102. Therefore, if the intervals of the read clock are short, then the frequency of the sine wave is high, and the stepping motor is driven at a high speed. Similarly, if the intervals of the read clock are long, the stepping motor is driven at a low speed. The UP/DOWN signal inverts the sign of the sine wave data read out from ROM 102 from plus to minus, or vice versa, and the stepping motor is driven in the opposite direction.

[0009] ROM 102 also stores data on duty ratios of rectangular waves corresponding to sine waves of 1/4 cycle, i.e. from 0 to π/2. Therefore, when data is read out from ROM 102, the address counter 101 controls the order for reading out data in a predetermined cyclic range and adds the positive or negative sign to the data as explained above, thereby to generate and output data for the full cycle from 0 to 2π.

[0010] Data on the duty ratios of rectangular waves corresponding to the sine waves is supplied to PWM generating circuits 103 and 104. The stepping motor to be driven here is of a 2-phase excitation type as stated above. Therefore, sine waves different in phase by π/2 are supplied simultaneously to the motor. Generation of waves in different phases can be realized by changing the way of reading data from ROM 102.

[0011] A rectangular-wave output from the PWM generating circuit 103 is supplied to the coil 107a of the stepping motor 107 via an H bridge circuit 105 for driving the stepping motor 107. A rectangular-wave output from the PWM generating circuit 104 is supplied to the coil 107b of the stepping motor 107 via an H bridge circuit 106. These rectangular-wave outputs are smoothed into sine waves (or cosine waves) by the H bridge circuit 105 and the coil 107a, or the H bridge circuit 106 and the coil 107b. Thus, driving of the stepping motor 107 by sinusoidal waves is realized.

[0012] Fig. 8 is a vector representation of the sine wave supplied to the stepping motor 107 driven in the above process. In the figure, arrows labelled phase A and phase B correspond to respective excitation vectors of two coils 107a and 107b. When sine and cosine waves are supplied to phase A and phase B, their composite vector draws a circle of a given diameter as illustrated.

[0013] In a video camera using such stepping motors, driving directions of the stepping motors are frequently changed for fine adjustment of focalization, or the like, during automatic focalization. Also during zooming function, rotating directions are frequently changed from one direction to the other. Moreover, if the camera includes the function of changing the zooming speed, a change in zooming speed causes a change in motor driving speed.

[0014] A large load is applied to a stepping motor under various conditions such as changes in driving direction, high-speed driving, starting of the motor, or low temperature, and if these conditions overlap, then the load to the stepping motor will become much larger. If, nevertheless, the driving voltage supplied to the stepping motor is not sufficiently large, then the motor cannot obtain a required torque, and invites so-called power swing.

[0015] In a conventional system using a stepping motor of this type, the driving voltage (or driving current) for driving the stepping motor is set to a value with which a torque large enough to prevent power swing can be obtained even when a maximum load is applied to the stepping motor, among others, used in the system. Then, the same drive voltage (or drive current) is supplied also under a small load. The torque necessary for the motor driven under a small load may be smaller than that under the maximum load. Therefore, the conventional system fails to optimise the driving efficiency.

[0016] If a stepping motor of this type is used in a portable video camera normally relying upon a battery to be charged from time to time, useless consumption of the battery is a great disadvantage.

[0017] US-A-4,851,755 discloses a stepper motor drive circuit in which a stepping detector is provided to determine whether the motor has actually stepped in response to the drive signal. If it has, the driving power is reduced, if it has not, the drive power is increased until it does.

[0018] JP-A-3-265,497 (and see US-A-5,418,443) describes a stepper motor drive circuit for use in a video camera, in which the memory storing data on the sine wave stores large amplitude sine wave data for use on start-up to provide a large starting torque.

[0019] It is an object of the invention to provide a portable video camera using stepping motors, in which the load to each motor is estimated and an appropriate driving voltage (or driving current) corresponding to the estimated load is supplied to the motor, in order to save power consumption by the stepping motors and to alleviate consumption of the battery.

[0020] According to the present invention there is provided a portable video camera using stepping motors for driving a zoom lens and a focussing lens, comprising:

drive signal generating means for generating drive signals for driving said stepping motors, each of said stepping motors being of a type using a sine wave as said drive signal (voltage and current) and wherein a memory is provided storing data on a sine wave;

   characterised by further comprising control means responsive to predetermined conditions affecting the loads on said stepping motors to control the drive signal generating means to vary drive voltages or drive currents of the drive signals in accordance with said predetermined conditions, said control means further comprising amplitude control means for controlling the amplitude of the sine wave to control the drive voltage or drive current. With the above constructions, since the stepping motors are driven in appropriate conditions variable with loads to the motors, power consumption by these motors can be reduced.

[0021] The invention will be further described by way of non-limitative example, with reference to the accompanying drawings, in which:-

Fig. 1. Is a block diagram showing an arrangement of a video camera to which the invention can be applied;

Fig. 2 is a diagram showing an example of sine waves corresponding to rectangular waves for driving motors efficiently;

Fig. 3 is a diagram showing a more detailed arrangement of a control circuit for a stepping motor in the.same embodiment;

Fig. 4 is a flow chart showing a process for determining an amplitude for driving the motors efficiently;

Fig. 5 is a diagram of representation of vectors of a sine wave supplied to a motor for driving the motor efficiently;

Fig. 6 is a diagram showing sine waves with different frequencies for different driving speeds;

Fig. 7 is a diagram showing an arrangement of a conventional circuit for driving a stepping motor; and

Fig. 8 is a diagram of representation of vectors of a sine wave supplied to a stepping motor by a conventional method.

[0022] An embodiment of the invention is described below with reference to the drawings. This invention is essentially directed to optimization of the driving voltage (or driving current) supplied to stepping motors by estimating loads applied to the motors.

[0023] Fig. 1 shows a general aspect of a video camera to which the invention can be applied. Numeral 1 denotes a zoom lens, and 2 a focusing lens. The zoom lens 1 is driven by a stepping motor used as a zooming motor 3. The focusing lens 2 is driven by a focusing motor 4. The zoom lens 1 is moved forward or backward along an optical axis by the zooming motor 3 to change the size of an image. The focusing lens 2 is moved forward or backward along the optical axis by the focusing motor 4 to establish focalization onto a desired image. Standard positions of the zoom lens 1 and the focusing lens 2 are detected by reset sensors 20 and 21, respectively, and a respective one of outputs from the reset sensors 20 and 21 are supplied to a zoom lens control circuit 12 and a focusing lens control circuit 13 which will be described later.

[0024] In this example, the stepping motors used as the zooming motor 3 and the focusing motor 4 are of a PM-type 2-phase excitation bipolar driving type.

[0025] An image from an object enters into CCD 5, used as a receptor element, through the zoom lens 1 and the focusing lens 2. Output signal from CCD 5 is supplied to S/H (sample-hold) AGC (automatic gain control) circuit 6 for extraction of a video signal and adjustment of the signal level. Output signal from the S/H AGC circuit 6 is converted into a digital signal in an A/D converter 7, and then supplied to a camera processor 8. The video signal supplied to the camera processor 8 is subjected to predetermined signal processing, and then sent to a video signal processor (not shown) provided at a later stage.

[0026] The camera processor 8 supplies a luminance signal (AFY signal) for automatic focalization to an auto-focusing detecting circuit 9. The auto-focusing detector 9 refers to the supplied AFY signal to determine whether focalization is established or not. The result of the determination is supplied as an estimated value to an auto-focusing control circuit 11 in MCU 10.

[0027] MCU 10 is a control circuit for controlling the entire system of the video camera, and contains a zoom lens control circuit 12 and a focusing lens control circuit 13 in addition to the auto-focusing control circuit 11.

[0028] The auto-focusing control circuit 11 evaluates the value of an output from the auto-focusing detecting circuit 9 and supplies the result of the evaluation to the focusing lens control circuit 13. The focusing lens control circuit 13 uses the evaluated value supplied from the circuit 11 to calculate, among others, how much the focusing lens 2 should be moved to establish focalization by driving the focusing motor 4, and supplies a control signal for controlling the motor in response to the required amount of movement and speed. The control signal is supplied as a focusing motor control signal to an adder 14.

[0029] The zoom lens control circuit 12 is supplied with a zooming command through buttons or other like means prepared on the video camera, for example, to instruct whether the object should be zoomed up or not, or at what speed the zoom lens should be driven. Then, a motor control signal responsive to the zooming command is output to move the zooming motor 3 according to a required amount of movement of the zoom lens, a required zooming speed, or a required zooming direction. The control signal is supplied to an adder 14 to serve as a zooming motor control signal.

[0030] In the adder 14, the focusing motor control signal and the zooming motor control signal are superposed at a predetermined timing and supplied to a serial transmission port 15. The supplied signal is sent to a pre-driver 16 for the zooming motor 3 and to a pre-driver 17 for the focusing motor 4. In each of these pre-drivers 16 and 17, the signal superposed in the serial signal at the predetermined timing for driving the associated motor is extracted. That is, the zooming motor control signal for driving the zooming motor 3 is extracted in the pre-driver 15, and the focusing motor control signal for driving the focusing motor 4 is extracted in the pre-driver 16.

[0031] The zooming motor 3 and the focusing motor 4 are driven by sine waves. Rectangular waves having duty ratios corresponding to sine waves to be used for driving the motors 3 and 4 are generated in the pre-drivers 16 and 17. By that time, the pre-drivers 16 and 17 are also supplied with the motor control signals responsive to the driving conditions as explained above. Then, the pre-drivers 16 and 17 make the rectangular waves to correspond to the control signals so as to drive the motors 3 and 4 efficiently.

[0032] As explained above, the load applied to each stepping motor varies with driving conditions.
Examples of relative magnitudes of the load are:

low-speed driving < high-speed driving

during driving in one direction < upon changing the direction

during driving in one direction < upon starting the motor

hot environment < cool environment

where the sign of inequality indicates the relation in magnitude between two operations or states.

[0033] Fig. 2 shows sine waves corresponding to rectangular waves for driving the motors efficiently. This figure comparatively shows a sine wave for driving the motor at a low speed and a sine wave for driving the motor at a high speed. The sine wave for low-speed driving has a smaller amplitude β than the amplitude α of the sine wave for high-speed driving, as expressed by α>β. That is, when the motor is driven at a low speed, the driving voltage (amplitude) is supplied with a value lower than that for driving the motor at a high speed. As a result, improvement in the motor driving efficiency is realized by supplying an appropriate driving voltage corresponding to the rotating speed. Assuming that low-speed driving is possible with 70% of the driving voltage required for high-speed driving, since the loss is proportional to the square of the voltage, taking the d.c. resistance of the coil alone into consideration, reduction of 51% in power consumption is realized.

[0034] In this manner, rectangular waves corresponding to the sine waves having amplitudes responsive to the loads varying with the operative conditions are supplied from the pre-drivers 16 and 17 to motor drivers 18 and 19. The motor drivers 18 and 19 comprise, among others, a bridge circuit for driving the stepping motor. Thus, the motor driver 18 drives the zooming motor 3, and the motor driver 19 drives the focusing motor 4. The rectangular waves supplied to the motor drivers 18 and 19 are smoothed into sine waves by the motor drivers 18, 19 and by coil circuits of the motors 3, 4.

[0035] Fig. 3 shows the arrangement of the control circuit for controlling the stepping motor used in this embodiment in greater detail. MCU 30 is coupled to an address counter 31. MCU 30 is also coupled to a VCA 41. The address counter 31 is coupled ROM 40 which stores data on sine/cosine waves with the amplitude of 100% alone such that an output from ROM 40 is supplied to VCA (voltage-controlled gain-controlled amplifier) 41 controlled by the AMP signal from MCU 30 such that the output is controlled in level as described below.

[0036] Externally suppled to the MCU 30 is a signal indicating conditions for driving the motor 36. Based on the supplied signal, an UP/DOWN signal for instructing the driving direction and a read clock signal for determining the driving speed are supplied to the address counter 31. Simultaneously, MCU 30 executes the process as explained with reference to the flow chart of Fig. 4. That is, a value determining the amplitude of the sine/cosine waves is increased or decreased in accordance with the conditions for driving the motor 36. The value determining the amplitude of the sine/cosine waves, which is obtained in this manner, is supplied to VCA 41 as a gain control signal (AMP signal). This is, for example, such that the amplitude of the sine/cosine waves for driving the motor 36 should be 75% of the maximum amplitude.

[0037] Data on the rectangular wave of a duty ratio corresponding to the sine/cosine waves preliminarily stored in ROM 40 is read out from MCU 30 by then address counter 31 which is supplied with the UP/DOWN signal and the read clock signal. The data read out here is supplied to VCA 41. Also supplied to VCA 41 is a value indicating the amplitude of the sine/cosine wave (AMP signal). According to this value, predetermined arithmetic operation is executed to the data supplied from ROM 40 to produce rectangular-wave data with a duty ratio corresponding to the sine/cosine waves with the amplitude of 75%, for example, and the data is supplied to the PWM generating circuits 34a and 34b. At this time, among data supplied from ROM 40, sine-wave data, for example, is supplied to the PWM generating circuit 34a, and cosine-wave data is supplied to the PWM generating circuit 34b.

[0038] A rectangular-wave output from the PWM generating circuit 34a is supplied to the coil 36a of the stepping motor 36 via the H bridge circuit 35a for driving the stepping motor 36. A rectangular-wave output from the PWM generating circuit 34b is supplied to the coil 36b of the stepping motor 36 via the H bridge circuit 35b. In this case, the rectangular wave is smoothed into a sine wave (or a cosine wave) by the H bridge circuit 35a and the coil 36a, or the H bridge circuit 35b and the coil 36b. As a result, the stepping motor 36 is driven by a sine or cosine wave. The motor 36 corresponds to the zooming motor 3 or focusing motor 4 explained above with reference to Fig. 1.

[0039] The address counter 31 is controlled by an UP/DOWN signal and a read clock signal from MCU 30. ROM 40 stores data of a duty ratio of a rectangular wave corresponding to a sine wave in the range of a quarter cycle. Therefore, when data is read out from ROM 40, the address counter 31 controls the order of reading data in the predetermined cyclic range and adds the positive or negative sign to generate and output data of one full cycle, that is, 0 to 2π.

[0040] Externally supplied to MCU 30 are signals indicating driving conditions for driving the motor 36. The signals include a user's entry signal for changing the zooming speed, a signal for adjusting focalisation, sent from the auto-focusing control circuit, or the like. The driving conditions here include, for example, the driving speed, inversion of the direction, reduction of the speed, and data on the temperature of the motor 36 and its environment, sent from a temperature sensor (not shown). MCU 30, in receipt of these signals, supplies a read clock signal for determining the driving speed and an UP/DOWN signal for inverting the direction to the address counter 31. The address counter 31, supplied with the clock read signal and the UP/DOWN signal, reads out the rectangular wave data corresponding to the sine/cosine wave stored in ROM 40 and sends it to the VCA 41.

[0041] Simultaneously, MCU 30 determines an amplitude for efficiently driving the motor 36. Fig. 4 is a flow chart of a process for this operation. First, at step S40, the speed for driving the motor 36 is determined. If the motor 36 is to drive the zoom lens, a user of the.camera selects; for example, one of high, middle and low zooming speeds, and enters his instruction through an external button or other like means.

[0042] The external input is sent to MCU 30, and MCU 30 determines an appropriate amplitude for sine/cosine waves for driving the motor 36 most efficiently with respect to the instructed driving speed. If the zoom lens is to be driven at a high speed, the process proceeds to step S41 where the amplitude is set to 9. If the zoom lens is to be driven at a middle speed, the process proceeds to step S42 where the amplitude is set to 8. If the zoom lens is to be driven at a low speed, the process proceeds to step S43 where the amplitude is set to 7. After an appropriate amplitude for the sine/cosine waves is chosen in step S41, S42 or S43 in response to the instructed driving speed, the process goes to step S44.

[0043] In step S44, it is determined from the signal supplied to MCU 30 whether the direction should be inverted or not. If not, the process goes directly to step S46. If the direction is to be inverted, since the load to the motor 36 increases, the process goes to step S45 where a new amplitude is determined by adding 1 to the amplitude determined in step S41, S42 or S43. Then the process proceeds to step S46.

[0044] In step S46, it is determined from the signal supplied to MCU 30 whether the driving speed should be reduced or not. If not, the process goes directly to step S48. If the speed should be reduced, since the load to the motor 36 decreases, the process goes to step S47 where a new amplitude is determined by subtracting 1 from the amplitude obtained in step S44. Then, the process goes to step S48.

[0045] In step S48, it is determined from the signal supplied from the temperature sensor (not shown) to MCU 30 whether the temperature of the motor 36 or its environment is higher or lower than a predetermined value. If the temperature is higher, the process goes directly to step S50. If the temperature is lower, since the load to the motor 36 increases, the process goes to step S49 where a new amplitude is determined by adding 1 to the amplitude obtained in step S46. Then, the flow goes to step S50.

[0046] In step S50. it is determined whichever sine/cosine waves should be applied to the value indicating the amplitude obtained by step S49. In this example, if the amplitude is equal to or larger than 10, then the process.goes to step S51 where sine/cosine waves with the amplitude of 100% is selected. If the amplitude equal 9, then the flow goes to step S52 where sine/cosine waves with the amplitude of 90% are chosen. If the amplitude is equal to or smaller than 8, then the flow goes to step S53 where a value indicating sine/cosine waves with the amplitude of 80% is selected. In this manner, an appropriate amplitude of sine/cosine waves for driving the motor 36 is obtained in accordance with the conditions for driving the motor 36.

[0047] Fig. 5 is a diagram of vector representation of a sine wave supplied to the motor 36 driven in the above-described manner. In the figure, arrows labelled with "A-phase" and "B-phase" correspond to vectors of magnetic excitation of two coils of each motor of a two-phase-excitation type. When a sine wave and a cosine wave are supplied to the A-phase and the B-phase, their composite vector draws a small vector orbit at a low speed and a large vector orbit at a high speed as illustrated.

[0048] In the flow chart of Fig. 4, four factors, namely, the driving speed, driving direction, reduction in speed and temperature of the motor and its environment, have been explained as conditions for driving the motor. However, the invention is not limited to this example, but may employ more additional factors. In such cases, one or more additional steps will be added prior to step S50 in the flow chart. These steps for processing the driving conditions may be in any desired sequence.

[0049] In the examples explained above, the stepping motor is driven by a constant voltage. The invention, however, may employ a constant current by providing a resistor in the H bridge to detect a current flowing in the motor coil and by feeding it back to the PWM generating circuit.

[0050] Additionally, the above description has been made on examples in which the stepping motor is driven by micro-step driving and in which the driving speed varies. The invention, however, is not limited to these examples. As to the driving waveform, the invention can be realized by using a rectangular wave used for two-phase excitation driving and 1-2-phase excitation driving and by similarly changing the amplitude.

[0051] Moreover, as to loaded conditions of the stepping motors, MCU may be designed to judge various factors, not limited to high-speed driving and low-speed driving.

[0052] As explained above, according to the invention, stepping motors for driving zoom and focusing lenses of a video camera can be supplied with appropriate drive voltages (or drive currents) responsive to loads to the stepping motors. Therefore, power consumption by the motors can be reduced. As a result, the battery can supply power for a longer time, and the portable video camera can be used for a long time.

[0053] Additionally, since the power consumed by the motors are optimized, generation of heat at the motors can be suppressed.

[0054] Further, since the motors are driven with minimum energy during low-speed driving, vibrations and noise of the motors can be reduced.

[0055] Having described specific preferred embodiments of the present invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope of the invention as defined in the appended claims.

Claims

1. A portable video camera using stepping motors (3, 4, 36) for driving a zoom lens (1) and a focussing lens (2), comprising:

drive signal generating means (18, 19, 34a-b, 35a-b) for generating drive signals for driving said stepping motors (3, 4, 36), each of said stepping motors (3, 4, 36) being of a type using a sine wave as said drive signal (voltage or current) and wherein a memory (40) is provided storing data on a sine wave;

   characterised by further comprising control means (16, 17, 30, 31, 32a-d, 33, 40, 41) responsive to predetermined conditions affecting the loads on said stepping motors (3, 4, 36) to control the drive signal generating means (18, 19, 34a-b, 35a-b) to vary drive voltages or drive currents of the drive signals in accordance with said predetermined conditions, said control means (16, 17, 30, 31, 40, 41) further comprising amplitude control means (41) for controlling the amplitude of the sine wave to control the drive voltage or drive current.

2. The portable video camera according to claim 1, wherein each of said stepping motors (3, 4, 36) is of a type which uses a sine wave as said drive signal (voltage or current) arid wherein a memory (32a-d) is provided storing data on sine waves with different amplitudes, whereby said control means (16, 17, 30, 31, 32a-d, 33) controls the drive voltage or drive current by selecting the data on one of said sine waves.

3. The portable video camera according to claim 1 or 2, wherein said control means (16, 17, 30, 31, 32a-d, 33, 40, 41) includes an address counter (31) to which read-out clocks and UP/DOWN signals are supplied from an MCU (30), a ROM (32a-d, 40) from which rectangular-wave data are read out in response to address data supplied from said address counter (31), and said drive signal generating means (18, 19, 34a-b, 35a-b) comprises a PWM generating circuit (34a-b) to which the rectangular-wave data output from said ROM (32a-d, 40) are supplied, a rectangular-wave output from said PWM generating circuit (34a-b) being supplied to said stepping motors (36) through H bridge circuits (35a-b).

4. The portable video camera according to claim 3, wherein said control means (16, 17, 30, 31, 32a-d, 33, 40, 41) responds to said predetermined conditions by means of said MCU (30).

5. The portable video camera according to claim 1, 2, 3 or 4, wherein said predetermined conditions comprise drive speeds, changes in direction, acceleration or deceleration, and environmental temperature.

Ansprüche

1. Tragbare Videokamera, die Schrittmotoren (3, 4, 36) zum Antrieb einer Zoomlinse (1) und einer Fokussierungslinse (2) verwendet, aufweisend:

eine Antriebssignalerzeugungseinrichtung (18, 19, 34a-b, 35a-b) zur Erzeugung von Antriebssignalen zum Antrieb der Schrittmotoren (3, 4, 36), wobei jeder der Schrittmotoren (3, 4, 36) eines Typs ist, der eine Sinuswelle als das Antriebssignal (Spannung oder Strom) verwendet, und wobei ein Speicher (40), der Daten bezüglich einer Sinuswelle speichert, vorgesehen ist,

gekennzeichnet durch weiter aufweisend: eine Steuereinrichtung (16, 17, 30, 31, 32a-d, 33, 40, 41), die auf die Lasten an den Schrittmotoren (3, 4, 36) beeinflussende vorbestimmte Bedingungen anspricht, um die Antriebssignalerzeugungseinrichtung (18, 19, 34a-b, 35a-b) zum Variieren von Antriebsspannungen oder Antriebsströmen der Antriebssignale entsprechend den vorbestimmten Bedingungen zu steuern, wobei die Steuereinrichtung (16, 17, 30, 31, 40, 41) außerdem eine Amplitudensteuereinrichtung (41) zur Steuerung der Amplitude der Sinuswelle zum Steuern der Antriebsspannung oder des Antriebsstroms aufweist.

2. Tragbare Videokamera nach Anspruch 1, wobei jeder der Schrittmotoren (3, 4, 36) eines Typs ist, der eine Sinuswelle als das Antriebssignal (Spannung oder Strom) verwendet, und wobei ein Speicher (32a-d), der Daten bezüglich Sinuswellen mit differenten Amplituden speichert, vorgesehen ist, wobei die Steuereinrichtung (16, 17, 30, 31, 32a-d, 33) die Antriebsspannung oder den Antriebsstrom durch Wählen der Daten bezüglich einer der Sinuswellen steuert.

3. Tragbare Videokamera nach Anspruch 1 oder 2, wobei die Steuereinrichtung (16, 17, 30, 31, 32a-d, 33, 40, 41) einen Adressenzähler (31), dem Auslesetakte und AUF/AB-Signale von einer MCU (30) zugeführt sind, einen ROM (32a-d, 40), von dem Rechteckwellendaten in Reaktion auf vom Adressenzähler (31) zugeführte Adressendaten ausgelesen werden, aufweist, und wobei die Antriebssignalerzeugungseinrichtung (18, 19, 34a-b, 35a-b) eine PWM-Erzeugungsschaltung (34a-b), der die vom ROM (32a-d, 40) ausgegebenen Rechteckwellendaten zugeführt sind, aufweist, wobei eine von der PWM-Erzeugungsschaltung (34a-b) ausgegebene Rechteckwelle den Schrittmotoren durch H-Brückenschaltungen (35a-b) zugeführt wird.

4. Tragbare Videokamera nach Anspruch 3, wobei die Steuereinrichtung (16, 17, 30, 31, 32a-d, 33, 40, 41) auf die vorbestimmten Bedingungen mittels der MCU (30) anspricht.

5. Tragbare Videokamera nach Anspruch 1, 2, 3 oder 4, wobei die vorbestimmten Bedingungen Antriebsgeschwindigkeiten, Änderungen in einer Richtung, Beschleunigung oder Verzögerung und Umgebungstemperatur umfassen.

Revendications

1. Caméra vidéo portative utilisant des moteurs pas à pas (3, 4, 36) pour entraîner une lentille à focale variable (1) et une lentille de mise au point (2), comprenant :

des moyens de génération de signal d'attaque (18, 19, 34a-b, 35a-b) pour générer des signaux d'attaque pour entraîner lesdits moteurs pas à pas (3, 4, 36), chacun desdits moteurs pas à pas (3, 4, 36) étant d'un type utilisant une onde sinusoïdale comme ledit signal d'attaque (tension ou courant) et dans laquelle une mémoire (40) est prévue stockant des données sur une onde sinusoïdale ;

   caractérisée en ce qu'elle comprend en outre des moyens de commande (16, 17, 30, 31, 32a-d, 33, 40, 41) sensibles à des états prédéterminés affectant les charges sur lesdits moteurs pas à pas (3, 4, 36) pour commander les moyens de génération de signal d'attaque (18, 19, 34a-b, 35a-b) pour modifier les tensions d'attaque ou les courants d'attaque des signaux d'attaque selon lesdits états prédéterminés, lesdits moyens de commande (16, 17, 30, 31, 40, 41) comprenant en outre un moyen de commande d'amplitude (41) pour commander l'amplitude de l'onde sinusoïdale pour commander la tension d'attaque ou le courant d'attaque.

2. Caméra vidéo portative selon la revendication 1, dans laquelle chacun desdits moteurs pas à pas (3, 4, 36) est d'un type qui utilise une onde sinusoïdale comme dit signal d'attaque (tension ou courant) et dans laquelle une mémoire (32a-d) est prévue stockant des données sur des ondes sinusoïdales avec différentes amplitudes, moyennant quoi lesdits moyens de commande (16, 17, 30, 31, 32a-d, 33) commandent la tension d'attaque ou le courant d'attaque en sélectionnant les données sur une desdites ondes sinusoïdales.

3. Caméra vidéo portative selon la revendication 1 ou 2, dans laquelle ledit moyen de commande (16, 17, 30, 31, 32a-d, 33, 40, 41) comprend un compteur d'adresses (31) auquel des horloges de lecture et des signaux HAUT/BAS sont transmis à partir d'un MCU (30), une ROM (32a-d, 40) à partir de laquelle des données d'onde rectangulaire sont affichées en réponse aux données d'adresses transmises à partir dudit compteur d'adresses (31), et ledit moyen de génération de signal d'attaque (18, 19, 34a-b, 35a-b) comprend un circuit de génération de MLI (34a-b) auquel la sortie de données d'onde rectangulaire de ladite ROM (32a-d, 40) est transmise, une sortie d'onde rectangulaire dudit circuit de génération de MLI (34a-b) étant transmise auxdits moteurs pas à pas (36) à travers des circuits avec un pont en H (35a-b).

4. Caméra vidéo portative selon la revendication 3, dans laquelle ledit moyen de commande (16, 17, 30, 31, 32a-d, 33, 40, 41) répond auxdits états prédéterminés au moyen dudit MCU (30).

5. Caméra vidéo portative selon la revendication 1, 2, 3 ou 4, dans laquelle lesdits états prédéterminés comprennent les vitesses d'entraînement, les changements de direction, l'accélération ou la décélération, et la température environnante.

Drawing